The present invention relates to a method for producing at least one welded joint between at least a first electrical conductor such as a rigid flat support, and at least a second electrical conductor such as litz wires, where the conductors are inserted into a compression space surrounded by limiting elements that can be adjusted relative to one another, and in which they are welded by means of an ultrasound welding device sonotrode which produces ultrasonic vibrations and forms one of the limiting elements.
In order to ultrasonically weld litz wires on a support, according to DE-C-34 37 749 it is provided that the cheeks limiting a compression space laterally can be displaced along the support, whereas the clearance of the cheeks is adjusted to the width of a section of a star sonotrode that dips into the compression space. The support itself is supported on a counter electrode, also called an anvil.
DE-Z.: Die Bibliothek der Technik, Band 108: Ultraschall-Metallschweiβen, Verlag Moderne Industrie, (The Library of Technology, vol. 108: Ultrasonic Metal Welding, Moderne Industrie Publishing), 86895 Landsberg, 1995, page 43, shows a weld between a U-shaped cable lug and electrical conductors. For this purpose, ultrasonic welding devices are used, in which the conductors to be welded are inserted into a compression space that is limited in a known manner by sections of a sonotrode and anvil as well as laterally displaceable cheeks.
From WO-A-95/10866 a method is known for compressing and subsequent ultrasonic welding of electrical conductors, in particular litz wires, in a compression space that can be adjusted to the height and width of the conductor, whereby the conductors to be welded are first compressed and then welded. The compression space can be adjusted to a specified height-width ratio independently of the cross section of the conductor to be welded.
Compression spaces of ultrasonic welding devices that are adjustable in height and width are likewise apparent from EP-B-0 143 936 or DE-A-37 19 083.
The power rating of each of the ultrasonic welding devices that are used is designed for the maximum cross section of the conductors to be welded. If usually control cables, for example, are to be connected to a connector, also called a terminal, the power rating of the ultrasonic welding device to be used is designed for the cross section of the control cables to be welded. If an earth cable is also to be connected, it is connected to the terminal in a conventional manner by means of screws or plugs. The disadvantage of the corresponding connection is that contact resistances may appear, which may disturb the signals of the control cables.
But even if the power of the ultrasonic welding device is sufficient to weld an earth cable or battery cable, for example, to a control cable on a connector, there are still disadvantages in that adequate process monitoring is not possible, because the permissible tolerances when welding conductors with large cross sections are frequently larger than the cross sections of the control cables, so that combination errors could consequently appear that cannot be detected in process monitoring.